1. Field of the Invention
The present invention is directed toward an apparatus for detecting the presence of a wrap accumulation of yarn on the surface of a heated or unheated roll in a synthetic yarn processing apparatus.
2. Description of the Prior Art
All textile processes handling yarn under tension have some level of broken filaments that can create roll wraps, especially when a plurality of yarn lines in a generally planar warp array are being processed by surface contact with a plurality of rolls. The processing may frequently involve heating the rolls. The rolls are usually shiny to achieve high friction for the desired draw forces and intimate contact with the yarn for rapid heat transfer to the yarn. Often four or more rolls with various surface and friction properties are used in succession to heat the yarn to a processing temperature for a particular length of time. Because of the elastic nature of synthetic polymers, broken filaments that may occur from time to time tend to stick to the processing rolls and accumulate thereon as wraps which may subsequently result in breaking of the yarn. Wrap detection is important for the commercial success of a warp machine for processing multiple yarns where the loss of a single end can cause the entire warp to shut down.
In an environment without automated assists, the detection of a wrap accumulation of yarn on a roll is a difficult matter. When a wrap occurs on a roll in a warp machine the operator must detect it quickly before a band of yarn greater than a predetermined threshold (typically, on the order of about one-eighth inch) accumulates on the roll. If left unattended the band might become so large that fluff would be created during removal, which would interfere with other yarn lines. The yarn may be white or another light color, providing little visual contrast with the surface of the roll, and making detection more difficult. Moreover, plural lines may break down at the same time due to process upsets. The operator needs to be able to identify which of a plurality of yarn lines are wrapping on the rolls so some appropriate action can be taken.
In view of the foregoing it is believed that there is a need for a system that will detect wrap accumulation on the surface of a roll. Such a system must be sufficiently robust so as to survive in the hot finish-laden atmosphere surrounding the hot rolls and must be affordable, reliable, and easily maintained. Of particular importance is the need to detect a wrap of one or several of a plurality of individual moving yarn lines on the surface of a roll and provide a suitable signal to an operator or an automated system so corrective action for the individual line or lines can be taken without disturbing the surrounding yarn lines. Such a sensor system needs to be adapted for easy cleaning, and for operation in a failsafe manner in case of malfunction of the sensor or failure of the operator to respond.